Automatic test equipment (ATE) includes electronics for sending signals to, and receiving signals from, a device under test (DUT) in order to test the operation of the DUT. The ATE includes test instruments, such as digital test instruments for performing digital tests on integrated circuits. The test instruments typically reside on a test head. A device interface board (DIB), which is typically provided by the DUT manufacturer and not manufactured with the ATE, connects the test head, and thus the test instruments, to the DUT. Transmission lines pass through the DIB; however, the ATE does not know the electrical path length of those transmission lines. This information, however, can be useful for various purposes including, but not limited to, aligning signals and determining signal line continuity.
TDR (time domain reflectometry) may be used to align signals at the end of a transmission line or to determine electrical continuity. However, TDR may be unreliable under certain circumstances, e.g., when signal rise times exceed the electrical path length of a transmission line. Furthermore, the ATE may not be capable of performing a TDR measurement.